If it is not a null pointer and L = x1,...,x{k-1}, it,x_{k+1},xn, then L1 = x1,...,x{k-1} and L2 = it,x{k+1},...,xn if dir = before. If it is a null pointer, then L1 is made empty and L2 = L. Finally L is made empty if it is not identical to L1 or L2.